1. Technical Field
The invention relates to a pair of ophthalmic spectacles which is adapted for characterizing a direction of gaze of a wearer of the spectacles.
2. Description of the Related Art
There are many existing systems for detecting the eye movements of a subject in real time. For example, U.S. Pat. No. 5,966,197 describes a system for laser ablation eye surgery, which detects and compensates for the eye movements of a patient. This system forms an image of the eye, and its rotational position within the socket is tracked by identifying the position of the limbus in the image. The limbus is the border between the sclera and the iris of the eye, and it can easily be detected in an image of the eye in near infrared light at wavelengths between 900 nm (nanometers) and 1200 nm. The sclera has a high light reflection coefficient of about 90% in this spectral domain, while the iris has a lower reflection coefficient of about 40%.
Other systems for detecting eye movements also exist, intended for use by patients in the conscious state. Some of these other systems consist of devices to be placed on the subject's head, and form images of the two eyes while the subject is looking at objects in his environment. Although a subject wearing one of these devices can remain mobile, these devices are not usable in everyday life but are to limited to use in sessions in which measurements of the subject are collected.
Certain applications require eye movement detection systems which are compatible with mobile use. There is therefore a need for an eye movement detection system which is both light and aesthetically pleasing, and which is not uncomfortable for the subject during prolonged use in everyday life. In addition, such a system is preferably low in cost to allow equipping a large number of individuals. There are currently no such eye movement detection systems in existence which meet these requirements in a satisfactory manner.